Fuse constructions including stress reducing means



J. H. SPROW May 31, 1966 FUSE CONSTRUCTIONS INCLUDING STRESS REDUCING MEANS Filed 001;. 4, 1963 4 Sheets-Sheet 1 Fig.3.

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May 31, 1966 J. H. SPROW 3,254,182

FUSE CONSTRUCTIONS INCLUDING STRESS REDUCING MEANS Filed Oct. 4, 1963 4 Sheets-Sheet 5 Fig.lO.

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May 31 ,1956 I s ow 3,254,182

FUSE CONSTRUCTIONS INCLUDING STRESS REDUCING MEANS Filed Oct. 4, 1963 4 Sheets-Sheet 4 LQ I7 I7 Fig". 65

l 7 SEC 5 1 I 37 1/ 37 f7 f 50. Q 7 E 5 l4 5? E 3,254,182 FUSE CONSTRUCTIONS INCLUDING STRESS REDUCING MEANS James H. Sprow, Monroeville, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 4, 1963, Ser. No. 313,836 8 Claims. (Cl. 200-120) This invention relates to fuse constructions in general, and, more particularly,.to fuse constructions utilizing a retracting arcing-rod construction.

A general object of the present invention is to provide an improved fuse construction of the type wherein an arcing rod is retracted during fuse rupture to elongate an are within an elongated fuse bore.

Another object of the present invention is to provide an improved fuse construction of the type wherein an arcing rod makes contacting engagement between a pair of spaced contact assemblies and is mechanically held against spring tension by a fusible means fusible upon a predetermined overload current.

Still a further object of the present invention is to provide an improved fuse construction wherein relatively high-value fault currents are established within an annular bore, and relatively low-value overload currents are established longitudinally within an elongated hollow tube defining the inner periphery of said annular bore.

A further object of the present invention is to provide an improved fuse construction employing a plurality of identical parts for a particular voltage rating and, for such a particular voltage rating only the fusible elements need be selected for the particular current rating desired.

Still a further object of the present invention is to provide an improved fusible construction in which strain upon the strain wire is minimized to prevent faulty operation.

In United States patent application filed September 30,

1963, Serial No. 312,727 by Russell E. Frink, and assigned to the assignee of the instant invention, entitled Fuse Constructions, there is disclosed and claimed a novel fuse construction wherein annular bore means are provided, along which moves, during interruption, a movable tubular arcing rod spring-biased in the opening direction, and mechanically held in the closed position by seriallyrelated fusible elements. There is also taught in the aforesaid Frink patent application the concept of utilizing an elongated gas-evolving tube defining the inner periphery of the annular bore means, and accommodating a pair of overlapping fusible elements particularly adapted for low-current interruption, and functioning to separate following separation of the main arcing tube an adequate distance to withstand the voltage.

According to the aforesaid Frink fuse construction, during relatively low-value overload currents the fusible means fuses to thereby release the arcing rod, and the subsequent separation of the overlapping low-current fusible elements will initially cause arc elongation within the inner tubular gas-evolving fuse tube. Intimate association of the relatively low-value arc with the inner walls of the inner gas-evolving fuse tube is thereby obtained to quickly effect such low-current arc interruption. In the case, however, where relatively high-value fault currents United States Patent 3,254,182 Patented May 31, 1966 are encountered, the construction of the aforesaid Frink fuse structure is to cause a relatively high are voltage to occur within the inner fuse tube to thereby cause a flashover externally of the inner fuse tube in the annular bore means between the arcing end of the main movable arcing rod and the terminal contact structure. In such eventuality, the relatively high-value fault current is interrupted within the relatively large cross-sectional area annular fuse-bore'means, and the pressure is thereby limited by the additional cross-sectional area of the fuse bore utilized. It is, accordingly, a further object of the present invention to improve upon the fuse construction set forth in the aforesaid Frink patent application rendering the same more reliable in operation, of more economical manufacture and minimizing any tensile stress imposed upon the fusible elements.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 is a perspective view of a fuse unit embodying the principles of the present invention, and illustrated in the closed current-carrying condition;

FIG. 2 is a longitudinal sectional view taken through the improved fuse-tube structure of the present invention with the fusible elements shown in their intact condition;

FIG. 3 is an end elevational view of the fuse-tube structure of FIG. 2;

FIG. 4 is a side elevational view, partially in vertical section, of the plunger assembly utilized in the fuse-tube construction of FIG. 2;

FIG. 5 is an end elevational view of the fuse plunger assembly of FIG. 4;

FIG. 6 is a top view of the fuse base or stationary fuse block;

FIG. 7 is a side elevational view of the pivotallymounted release tube;

FIG. 8 is a side elevational view of the improved biasing-spring construction of the present invention;

.FIG. 9 is a side elevational view of a typical fuse element employed in the improved fuse construction of the present invention;

FIG. 10 is a side elevational view, partially in vertical section, of the arcing-tube assembly of the present invention;

FIG. 11 is a fragmentary view illustrating the location of the several elements and the disposition of the arc during high-current interruption;

FIG. 12 is a fragmentary sectional view illustrating the disposition of the several parts and the location of the are drawn during low-current interruption;

FIG. 13 illustrates a modified type of biasing-spring arrangement exerted on the pivotally-mounted release tube.

Referring to the drawings, and more particularly to FIG. 1 thereof, the reference numeral 1 generally designates a high-voltage high-power drop-out type of fuse structure, the general arrangement of which is set forth in the United States Patent 2,403,121, issued July 2, 1946 to Herbert L. Rawlins et a1. As shown, the fuse structure 1, includes a base 2 formed of sheet metal, and a pair of outwardly-extending insulator supports 3, 4. The upper insulator support 3 serves to support fixedly in position a break jaw 5, the details of which are shown in FIGURE 1 of the aforesaid patent.

Supported from the lower insulator support 4 is a hinge jaw 6 which pivotally supports a fuse unit 7, in-

teriorly of which extends fusible elements and latching means, more fully described hereinafter. As shown in FIGURE 1, the fuse unit 7 serves to electrically bridge the break jaw contact 5 and the hinge jaw contact 6 so that current will pass therebetween by way of terminal pads 8, 9, to which the external circuit L L is connected.

The fuse unit 7 generally comprises a replaceable fuse structure 10, more clearly shown in FIG. 2, and a pair of end fuse fittings 11, 12 (FIG. 1). The upper end fuse fitting 11 comprises an operating eye 11a, and is, as well known by those skilled in the art, utilized for effecting opening and closing movement of the fuse unit 7 by means of a conventional hook-stick (not shown).

The lower fuse fitting 12 (FIG. 1) comprises a hinge lifting eye 12a, which may be employed in conjunction with the aforesaid switch-stick to effect physical removal of the fuse unit 7 from the hinge jaw contact 6 for re-' placement of the fuse unit 7.

With reference to FIG. 2 of the drawings, it will be noted that the fuse structure comprises a fuse tube 13 of insulating material, such as fibre, synthetic resin, or the like, and the opposite .ends of the fuse tube 13 are adapted to be closed by end terminal-caps, or fuse ferrules 14, 15, as well known by those skilled in the art. The fuse ferrules 14, 15 may be rolled into indentations 13a of the fuse tube 13, and securely fastened into position by staking pins, so that the end fittings 11, 12, when encircling the ferrules 14, 15, and clamped into position, will securely engage the fuse-tube structure 10 without loosening.

As shown more particularly in FIG. 2, the fuse ferrules 14, 15 constitute fuse-terminal means, or fuse terminals, which are spaced longitudinally of the fuse tube 13 and have an'insulating section A disposed therebetween. Such an insulating section A includes not only the pertinent portion of the fuse-tube wall 13, but

also a plurality of ring-shaped blocks 17 composed ofa suitable gas-evolving material, such as boric acid, fibre, or embodying high molecular weight polyoxymethylenes and sold under the trade name Delrin. US.

Patent 3,059,081 Gainer et al. claims such air arc-extinguishing material. The utilization of the annular gasevolving blocks 17, in conjunction with an inner gasevolving tubular member 18, more particularly shown in FIG. 4, constitutes an annular longitudinally-extending fuse-passage means 19, within which relatively highvalue fault currents are interrupted, as more particularly described hereinafter.

Movable longitudinally of the fuse-tube structure 10 is a tubular arcing rod 20 having an arcing portion 20a at one end thereof, and having an enlarged portion 20b thereof, which is crimped over an ejector stop, or fuserod extension portion 21, which iseifective to project through an aperture 22 of a plug 22a threaded into the upper fuse ferrule 15, and capable of actuating a kickout, or ejector mechanism disposed interiorly of the hood 5a (FIG. 1), and more particularly described in detail in the aforesaid Rawlins patent. The particular ejector mechanism, which is triggered by the projection of the ejector stop 21, constitutes no part of the present invention, and reference may be had to the aforesaid Rawlins patent for further details thereof. As well known by those skilled in the art, upon actuation of such an ejector mechanism disposed within the hood 5a of the upper break-jaw contact 5, the fuse structure 10 .is rotated about the lower hinge jaw 6 and is dropped downwardly substantially 180 to provide an air break in the circuit following fuse rupture.

With further reference to the tubular arcing rod 20, as shown in FL 10 of the drawings, it will be noted that a strain member 23 is secured thereto by threading through an aperture 21a of the ejector 21, and brazed I a sleeve, which is brazed to the extremity of the strain member 23. In accordance with the present invention, suitable primary, or first biasing means 26 are utilized to effect opening upward motion of the tubular arcing rod 20, as viewed in FIG. 2 of the drawings. More particularly, the primary biasing means 26 assumes the form of a helical tension spring 27 having some end turns 27a captive to the rear side of an enlargement 21b of the ejector rod 21, which provides a seat therefor. The upper end turns 27b of the helical tension spring 27 are seated within an apertured cup-shaped spring seat 28, disposed Within a recess 29 of the end fuse ferrule 15, and having a radially outwardly extending flange seat 28a abuttingly engaged by the apertured fuse plug 22a. As a result, the tubular arcing rod 20 is constantly biased toward the upwardly opening position, and is latched in the closed position, as shown in FIG. 2, by a latching means 30 comprising the aforesaid releasable member 24, and abutment means 32 defining a stationary latch surface 34, or shoulder portion, against which the releasable member 24 is releasably engaged, as shown in FIG. 2 of the drawings.

The aforesaid abutment means 32 preferably assumes the form of a stationary contact block 36 (FIG. 4) fixedly secured, by bolts 37, to the side wall of the fuse tube 13. The stationary contact block 36, in addition, is provided with a recessed portion 36a, into which is inserted, and suitably secured, a supporting end portion 18a of the inner gas-evolving interrupting tube 18. Reference may be had to FIGS. 4-6 in this connection.

As shown more in detail in FIGS. 5 and 6 of the drawings, the stationary contact block 36 is provided with a pair of spaced support ears 36b, between which is pivotally supported, by means of a pivot pin 38, an actuating means, in this particular instance assuming the form of an insulating tube 41, and shown more in detail in FIG. 7 of the drawings.

As illustrated more clearly in FIG. 4 of the drawings, a fusible release link 42, in one particular instance assuming the form of 25 mil Nichrome wire is looped about the pivot pin 38, and extends out of the open outer end of the releasing member 41 and is fixedly secured to a terminal bolt 44, as shown in FIG. 2 of the drawings. It will be noted that the terminal bolt 44 is threaded into a tapped aperture 14a of the end fuse ferrule 14 so as to make electrical contact therewith.

Suitable secondary biasing means 46, assuming the form of a U-shaped spring 47, more clearly shown in FIG. 8 of the drawings, is employed to bias the pivotallysupported actuator 41 in a clockwise releasing direction about the pivot pin 38, as viewed in FIG. 2 of the drawings. This releasing biasing action, is however, counteracted by the securement of the releasing fuse link 42 to the terminal bolt 44.

A main series fuse link 50 is provided, the configuration of which is more clearly illustrated in FIG. 9 of the drawings. As shown in FIG. 2, the main series fuse link 50 is secured by a plurality of bolts or screws (not shown) to the fuse terminal, or ferrule 14 and to the inner sidewall 52a of a sleeve-like contact cylinder 52. As shown, the contact cylinder 52 is slotted, as at 5211, and several of the slotted portions are bent inwardly to form a plurality of contact fingers 52c. Preferably, the plurality of circumferentially-disposed contact fingers 52c are biased radially inwardly by a plurality of garter helical springs 53.

As shown in FIG. 2, the several contact fingers 52c make contacting engagement with the external side wall of the arcing extremity 20a of the arcing tube 20.

To assist in minimizing the formations of corona adacent the sharp corners of the contact fingers 52c, preferably there is provided a cup-shaped corona cap 54,

'5 which is disposed immediately adjacent the lowermost gas-evolving extinguishing block 17, and held in position by several of the intervening slotted portions 52b which are unbent.

With reference to FIG. 4 of the drawings, it will be observed that the abutment means, or relatively stationary contact block 36, has a bore 55 longitudinally provided therein, which is in registry with the bore 56 provided within the low-current interrupting tube 18. As will be more fully explained hereinafter, during fuse operation, the strain element 23, with the releasing member 24 attached thereto, is withdrawn axially through the bore 55 of the contact block 36 and axially longitudinally in an upward direction, as viewed in FIGS. 2 and 4, through the bore 56 of the low-current interrupting tube 18. An arc will, consequently, be established between an arcing portion 58 of the stationary contact block 36 and the strain wire, 23, as shown more clearly in FIG. 12 of the drawings.

To prevent excessive pressure being established interiorly of the low-current interrupting tube 18, and moreover to permit a ready transfer of the are from the region interiorly of the tube 18 to the region 19 exteriorl'y of the interrupting tube 18, there is provided a plurality of venting holes 18a provided at spaced points along the lowcurrent interrupting tube 18. By way of example, and not by way of limitation, the apertures 18a are disposed one inch apart and are /8 inch in diameter.

Disposed adjacent the upper end of the fuse structure 10, with reference to FIG. 2, is a relatively stationary contact structure 59 comprising a plurality of inwardlybent finger portions 60a of a slotted contact tube 60, the construction being very similar to that being previously described in connection with the relatively stationary contact structure 48 associated with the arcing end 20a of the movable interrupting tube 20. As shown more in detail in FIG. 2, the metallic contact tube 60 has several finger portions 600 bent inwardly, and biased radially inwardly by garter springs 53. Intervening finger portions 60b are utilized to hold into position a second cup-shaped corona cap 54 identical to the corona cap 54 previously described. The function therefor is the same as described hereinbefore. Additionally, the relatively stationary con tact tube 60 has an end outwardly-extending flange portion 60c, which is interposed between the flange portion 28a of the spring seat 28 and a shoulder portion 62 of the fuse terminal, or ferrule 15, as shown in FIG. 2.

FUSE OPERATION It will be obvious that in the intact condition of the fuse structure 10, as illustrated in FIG. 2, the current path therethrough comprises fuse terminal 15, plug member 22a, fiange portions 28a, 62 through the contact tube 60, through finger portions 60a thereof. The current then passes through the enlarged portion 20b of the arcing tube 20 to the finger portions 520, and thence through the lower relatively stationary contact tube 52 to the upper mounting block 50:: of the main series fuse link 50. The current then passes through the fusible portion 50b of the fuse link 50, through the fuse block 500 and by way of the conducting screws 51 to the lower fuse terminal or ferrule 14.

The main series'fuse link 50 is selected from a variety of available fuse links for the particular current rating for the fuse under consideration. When the series current exceeds the predetermined value for which the fuse link 50 is rated, the fuse link 50 will fuse or rupture, and, because of the gap G provided between the outer extremity 52e of the contact tube 60 and the inwardly extending portion 14b of the ferrule terminal 14, the current will be compelled to \pass through the electrically-parallel releasing fuse link 42, which will thereupon immediately rupture. The fusion, or rupture of the releasing fuse link 42 will immediately permit the secondary biasing spring 47 to rotate the pivotally-mounted actuator 41 and thereby a eifec-t release of the releasable member 24 off of the latching surface 34 of the abutment means, or relatively stationary contact block 36 to thereby effect release of the arcing tube 20.

By virtue of the biasing action exerted by the helical tension spring 27, the arcing tube 20, upon release thereof by release of the latching means 30, will quickly move upwardly, as viewed in FIG. 2, providing rapid separation between the arcing portion 20a thereof and the contact fingers 52c, and at the same time carrying therewith the strain wire 23 through the bore 55 of contact block 36 and longitudinally through the bore 56 of low-current arcing tube 18.

If the magnitude of the fault current being interrupted is relatively low, the arc 63 is entirely established within the bore 56 of the gas-evolving low-current interrupting tube 18, and are extinction occurs entirely therewithin, as shown more clearly in FIG. 12 of the drawings.

If, on the other hand, the are being drawn is relatively large, due to a high-magnitude fault current existing in the protected line, the ionized arc gases will pass through the apertures 18a and into the annular region 19 to transfer the are into the larger outer annular arc passage 19 and will be extinguished within this passage. FIG. 11 of the drawings more clearly shows the arc 65 having been transferred to the arcing portion 20a of arcing tube 20 and the contact fingers 52c of the relatively stationary contact structure 48. There is, thereby, achieved a selective operation distinguishing between high currents and low currents and providing suitable arc-extinguishing means for effecting extinction of the particular current being interrupted.

As more fully brought out in the aforesaid Frink patent application, for interrupting high-magnitude fault currents an adequate arcing-passage cross-sectional area is necessary to prevent undue pressure and possible explosion of the fuse-tube structure. For the interruption of relatively low currents, however, if the arc passage is too large, there does not occur an intimate enough contact betwen the arc and the adjacent gas-evolving material to provide an adequate amount of deionizing arc gases being evolved from the gas-evolving material. It is, therefore, necessary to provide a relatively small cross sectional area are passage for the effective interruption of low-value currents, and, as was the case in the aforesaid Frink application, in the instant application the relatively restricted low-current fuse bore 56 provides this desirable action.

From the foregoing it will be apparent that low-current interruption, say up to substantially amperes on a 69 kv. fuse structure of 2 million kva. interrupting capacity and interrupting 18,000 amperes on a symmetrical basis, is achieved entirely within the restricted bore 56 of the inner low-current interrupting tube 18, whereas currents in excess of this estimated value of 100 amperes are interrupted in the annular arcing passage 19 exter'iorly of the low-current interrupting tube 18 due to the transferring action previously referred to.

The fuse structure 10 of the present application is particularly suitable for a wide range of voltages. For example, the fuse structure is suitable for voltage ranges of 46, 69, 92, and 138 kv. rating. For each voltage rating, as mentioned hereinbefore, all of the structural parts are identical with the exception of the particular main series fuse link 50 being utilized. A wide range of current values, say from /2 ampere to 300 amperes, are available, and may readily be interchanged within the same fuse structure 10.

A few of the important advantages of the present invention are as follows:

(1) Due to the mechanical advantage gained by the use of restraining lever 41 and the method of holding the strain wire 23, the fusible release wire 42 can be made smallenough for low-current ratings, while minimizing 7 possibility of damage due to accidental mechanical jars, or shocks.

(2) There results the avoidance of possible failure of the fuse due to the fuse element catching in the bore during interruption, as has been the case in the prior-art structures.

(3) Heat damage to the fuse-lining material is avoided by removing the fusible elements 42, 50 to a point away from such lining.

(4) Since the main series fusible element 50 is removable, the current rating of the fuse can be changed readily merely by changing this particular element. 1

(5) The entire fuse structure may be disassembled, examined and reassembled without destruction of the several parts.

(6) The design of the strain wire 23, releasable sleeve 24 and releasing lever 41 is such as to positively hold the latching means in the proper position regardless of shock until fuse operation calls for such releasing action to take place.

The use of the holes 18a, provided in the low-current gas-evolving arcing tube 18, not only relieves the pressure built up inside of the bore 56 of the interrupting tube 18, but also prevents this tube 18 from expanding and rubbing inside of the moving outer tubular electrode rod 20. Such expansion would slow down the moving tube 20 and conceivably might cause a failure. In addition, the holes 18a permit the ionized gas to escape from the central bore 56 of the low-current interrupting tube 18 to the outer annular bore 19, and cause the transfer of the arc to the outer bore when the current is too large to be extinguished within the central bore 56.

From the foregoing description it will be apparent that there is provided a novel type of fuse structure 10 providing a desired selective operation to bring about the most etficient interrupting conditions dependent upon the value of the particular fault or overload current being interrupted. During heavy fault current interruption, the arc is lengthened within the outer annular fuse bore 19 between the contact fingers 52c and the arcing portion 20a of the arcing tube .20, as shown in FIG. 11.

Gas is evolved not only from the outer lining defined by the stacked ring-shaped gas-evolving blocks 17, but also by the external surface of the inner interrupting tube 18. The gas is blasted along the fuse-tube structure and out through the venting aperture 70 of the lower fuse terminal or ferrule 14. During low-current interruption, as shown in FIG. 12, the relatively low-current arc is drawn within the restricted bore 56 in intimate association with the inner walls of the interrupting tube 18. Due to such intimate association, the requisite amount of gas is evolved from the fuse bore 56 of the low-current interrupting tube 18 to effectively interrupt such low-current arcs, and the evolved gas is vented out through the apertures 18a into the outer vented region 19, and out the end vent 70.

FIG. 13 shows a modified type of biasing spring construction 47a for the pivotally-supported releasing member 41. In this particular instance, there is utilized a tension spring 47a secured within an aperture 41a of the releasing tube 41, and a terminal bolt 76 threaded into a tapped opening of the modified-type fuse ferrule 114.

Although there have been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration and that changes and modifications may readily be made therein by those skilled in the art, without departing from the spirit and scope of the invention.

I claim as my invention:

1. .A fuse structure including afuse tube having spaced fuse terminals disposed adjacent opposite ends of the fuse tube, a movable arcing rod movable longitudinally interiorly of the fuse tube, means biasing the movable arcing rod toward one of the fuse terminals interrupting means disposed along the path of movement of the movable arcing rod to assist in effecting arc extinction, fusible means in series with said arcing rod and fusible above a predetermined current level carried by the fuse structure, said fusible means comprising a main series fuse link and a relatively high-resistance releasing fusible link, latching means for holding the arcing rod against the tension exerted by said biasing means including a strain member secured to the arcing rod and having a releasable member secured thereto, means defining a latch surface mounted on the fuse tube upon which said releasable member is releasably latched, and releasing means for said latching means including said releasing link, 'whereby passage of line current through the fuse structure above said predetermined current level will first effect fusion of the main series fuse link and thereby force the series line current through the releasing link to rupture the latter and effect release of said latching means.

2. The combination of claim 1, wherein the movable arcing rod is an open metallic tube, a relatively stationary low-current insulating interrupting tube is disposed interiorly of the open-ended movable tubular arcing rod, and said strain member is a wire retractable interiorly of said relatively stationary low-current interrupting tube.

3. The combination of claim 1, wherein a spaced pair of relatively stationary contact assemblies are disposed adjacent the spaced fuse terminals, and the movable arcing rod makes separable bridging contacting engagement with said spaced pair of relatively stationary contact assemblies.

4. The combination according to claim 1, wherein a spaced pair of relatively stationary contact assemblies are disposed adjacent the spaced fuse terminals, and the movable arcing rod makes separable bridging contacting engagement with said spaced pair of relatively stationary contact assemblies and the movable arcing rod is an open metallic tube, a relatively stationary low-current insulating interrupting tube is disposed interiorly of the openended movable tubular arcing rod, and said strain member is a wire retractable interiorly of said relatively stationary low-current interrupting tube.

5. A fuse structure including a fuse tube having spaced fuse terminals disposed adjacent opposite ends of the fuse tube, a relatively stationary contact assembly disposed inwardly of one fuse terminal and electrically isolated therefrom, a main series fuse link electrically bridging said relatively stationary contact assembly and said one fuse terminal, a low-current interrupting tube supported by the relatively stationary contact assembly and extending longitudinally of the fuse tube toward the other fuse terminal, a movable tubular open-ended arcing rod movable toward said other fuse terminal and enveloping at least partially said low-current interrupting tube, means biasing the movable tubular arcing rod toward said other fuse terminal, said arcing rod making contacting engagement with the relatively stationary contact means, interrupting means disposed along the path of movement of the movable tubular arcing rod to assist in arc extinction, a relatively high-resistance releasing fusible link in electrical parallel with said main series fuse link, latching means for holding the arcing rod against the tension exerted by said biasing means including a strain member secured to the arcing rod and passing through the bore of the low-current interrupting tube, said strain member having a releasable member secured to the end thereof, means on said relatively stationary contact assembly defining a latch surface upon which said releasable member releasably latched, and releasing means for said latching means including said releasing link, whereby passage of line current through the fuse structure above said predetermined current level will first effect fusion of the main series fuse link and thereby force the series line current through the releasing link to rupture the latter and effect release of said latching means.

6. The combination of claim 5, wherein the releasing fuse link holds a pivotally-mounted actuator from rotating to a releasing position .to free said releasable membet.

7. The combination of claim 5, wherein a contact block constituting a part of the relatively stationary contact means supports said low-current interrupting tube and in addition defines said latch surface.

8. The combination of claim 7, wherein the contact block has a bore therethrough in registry with the bore through the low-current interrupting tube.

Nordhem 200--120 X Smythe 200-117 McMahon et a1 200-417 Ramsey 200-117 McMahon et a1 200120 BERNARD A. GILHEANY, Primary Examiner. 0 

1. A FUSE STRUCTURE INCLUDING A FUSE TUBE HAVING SPACED FUSE TERMINALS DISPOSED ADJACENT OPPOSITE ENDS OF THE FUSE TUBE, A MOVABLE ARCING ROD MOVABLE LONGITUDINALLY INTERIORLY OF THE FUSE TUBE, MEANS BIASING THE MOVABLE ARCING ROD TOWARD ONE OF THE FUSE TERMINALS INTERRUPTING MEANS DISPOSED ALONG THE PATH OF MOVEMENT OF THE MOVABLE ARCING ROD TO ASSIST IN EFFECTING ARC EXTINCTION, FUSIBLE MEANS IN SERIES WITH SAID ARCING ROD AND FUSIBLE ABOVE A PREDETERMINED CURRENT LEVEL CARRIED BY THE FUSE STRUCTURE, SAID FUSIBLE MEANS COMPRISING A MAIN SERIES FUSE LINK AND A RELATIVELY HIGH-RESISTANCE RELEASING FUSIBLE LINK, LATCHING MEANS FOR HOLDING THE ARCING ROD AGAINST THE TENSION EXERTED BY SAID BIASING MEANS INCLUDING A STRAIN MEMBER SECURED TO THE ARCING ROD AND HAVING A RELEASABLE MEMBER SECURED THERETO, MEANS DEFINING A LATCH SURFACE MOUNTED ON THE FUSE TUBE UPON WHICH SAID RELEASABLE MEMBER IS RELEASABLY LATCHED, AND RELEASING MEANS FOR SAID LATCHING MEANS INCLUDING SAID RELEASING LINK, WHEREBY PASSAGE OF LINE CURRENT THROUGH THE FUSE STRUCTURE ABOVE SAID PREDETERMINED CURRENT LEVEL WILL FIRST EFFECT FUSION OF THE MAIN SERIES FUSE LINK AND THEREBY FORCE THE SERIES LINE CURRENT THROUGH THE RELEASING LINK TO RUPTURE THE LATTER AND EFFECT RELEASE OF SAID LATCHING MEANS. 